The present invention relates to an apparatus for accurately soldering electronic parts, such as ICs, LSIs, and other works, using a laser beam.
Techniques for soldering using a laser beam are well known, as disclosed in, for example, Japanese Unexamined Patent Application Publication Nos. 58-161396 and 63-137576. According to such techniques, a laser beam is projected onto the object to be soldered, such as a printed board, from a soldering head to melt the solder with heat therefrom. Thus, it has advantages such that soldering can be performed without coming into contact with the object.
In the soldering by the laser beam, first, the object to be soldered must be positioned so that the laser beam can be projected onto the object to be soldered while a proper positional relationship is held therebetween. For example, as shown in FIGS. 4(A) and 4(B), when metallic patterns 3, which are each printed around one of a plurality of connecting holes 2 on a printed board 1, are soldered to connector pins 5 of an electronic part 4, each of the connector pins being inserted in one of the connecting holes 2, positioning is performed so that a laser beam 6 is projected onto both the metallic pattern 3 and the connector pin 5 at a proper ratio, one of which is shown on an enlarged scale in FIG. 5, and a thread-like solder 7 is then supplied, thus, performing soldering.
Conventionally, during positioning, in the case where the laser beam has a visible light area, the laser beam is projected onto the object to be soldered, and the soldering head or the work is moved while the projected part is observed with the naked eye. In addition, in the case where the laser beam has no visible light area, the visible light is formed with a He-Ne laser or the like and is then projected imitatively, thus, the positioning is similarly performed while being observed with the naked eye.
The laser beam is, however, an extremely thin beam of light, the object to be soldered is also an extremely small point, and the operation space for soldering is small; accordingly, it is difficult for an operator to bring his face near the object to be soldered and to look straight at the part, so that the operator can only take a peep at it from a position diagonally above. Therefore, it is very difficult to position the laser beam while observing the object to be soldered with the naked eye, and thus, it is almost impossible to perform accurate and efficient positioning in a short time.
It is therefore a technical object of the present invention to allow positioning of a projection position of a laser beam to be easily and accurately performed in a short time, and to increase the accuracy of the subsequent soldering when the laser beam is projected onto the object to be soldered for soldering.
In order to achieve the above object, according to the present invention, there is provided a laser soldering method, characterized in that an image pickup camera is mounted on a soldering head for projecting a laser beam for soldering toward an object to be soldered in such a manner that an optical axis thereof coincides with that of the laser beam; and the camera images the object to be soldered and displays the image on a monitor screen, wherein a projection spot positioned on the optical axis of the laser beam is displayed on the monitor screen; wherein, while the positional relationship between the object to be soldered and the projection spot is observed on the monitor screen, the soldering head and the object to be soldered are moved relative to each other to position the projection spot; and subsequently, the laser beam is projected from the soldering head to the object to be soldered, thus, performing soldering.
According to the present invention, as described above, the positioning is performed while the positional relationship between the object to be soldered, which is displayed on the screen of the monitor on an enlarged scale, and the projection spot of the laser beam is observed. Thus, the positioning operation can be significantly accurately performed in a short time compared with the conventional method in which positioning is performed while the slight soldering point is observed with the naked eye from a position diagonally above. Consequently, the accuracy of soldering subsequent to that can be improved and the time required for the entire soldering operation can be significantly reduced, thereby improving the operating efficiency.
In the present invention, preferably, soldering is performed while a hot inert gas, which is heated to a specified temperature in advance, is ejected from a gas ejection nozzle provided at the soldering head along an optical axis of the laser beam. Thus, oxidation and rejection of solder can be reliably prevented and the soldering accuracy can be significantly improved.
According to the present invention, in order to embody the above described method, there is provided a laser soldering apparatus characterized by comprising: a soldering head for projecting a laser beam for soldering toward an object to be soldered; a laser mechanism connected to the soldering head; an image pickup camera mounted on the soldering head in such a manner that an optical axis thereof coincides with that of the laser beam; a monitor which displays an image of the object to be soldered, which is captured by the camera, on a screen, and which displays a projection spot of the laser beam on the screen; and a control device for moving the object to be soldered and the soldering head relative to each other.
In this instance, the soldering head may be supported by a movable arm, and the movable arm may be controlled by the control device.
The projection spot displayed on the monitor screen is indicated by a portion surrounded by two vertical parallel lines and two horizontal parallel lines, wherein the size of the projection spot is freely adjusted by changing the interval between the parallel lines.
In the soldering apparatus having the above described structure, since the image pickup camera is mounted on the soldering head in such a manner that the optical axis thereof coincides with that of the laser beam, and the soldering head is used for both projection of the laser beam and imaging by the camera, the structure is simple and streamlined, and the positioning of the projection spot of the laser beam to the object to be soldered can be easily and accurately performed. Also, immediately after completion of positioning, the soldering operation by the laser beam can be started; therefore, after positioning, there is no need to move the camera to another position where it is not used.
In the present invention, the soldering head includes a cylindrical casing having a projection aperture for projecting a laser beam at an end thereof, optical lenses disposed in the casing, and a half mirror disposed at a position nearer to a base end of the casing than to the optical lenses in such a manner that the half mirror is disposed at an angle of 45 degrees to the optical axis of the optical lenses, wherein a camera is mounted on the base end of the casing in such a manner that it can image the object to be soldered from the projection aperture via the half mirror and the optical lenses, and wherein an optical fiber for outputting the laser beam from a laser mechanism toward the half mirror is connected to a fiber connecting section formed at the side of the casing at a position corresponding to the half mirror.
The fiber connecting section may include switching means for switching the diameter of the laser beam which is output from the optical fiber.
Preferably, the soldering head includes a gas ejection nozzle for ejecting an inert gas along the optical axis of the laser beam, and a gas supply mechanism for supplying a hot inert gas, which is heated in advance, is connected to the gas ejection nozzle.